Speed limit c in the multiverse

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Discussion Overview

The discussion revolves around the factors influencing the speed of light in the context of a multiverse, particularly through the lens of string theory. Participants explore theoretical implications, definitions, and the nature of physical constants across different universes.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants question whether current understanding of string theory is sufficient to determine the factors that lead to varying speeds of massless fields in different multiverses.
  • One participant suggests that the speed of light is fundamentally a unit conversion, comparing it to asking about the number of inches in a foot within a multiverse context.
  • Another viewpoint emphasizes that the speed of light is defined within individual universes based on local measurements, such as "rods and clocks," and is influenced by geometric quantities in string theory, like the size of extra dimensions.
  • There is a proposal that the fine structure constant is more fundamental than the speed of light, implying that variations in this constant could lead to different speeds for massless objects.
  • One participant expresses a desire to understand the topic better, indicating a perception that their question may not have been well-formed.
  • A later reply reassures that there are no bad questions, only bad answers, encouraging continued inquiry.
  • Another participant reiterates that the speed of light is derivative and discusses the implications of using a single unit for time and space in the context of Lorentz transformations.

Areas of Agreement / Disagreement

Participants express differing views on the nature of the speed of light and its dependence on various factors, indicating that multiple competing perspectives remain without a clear consensus.

Contextual Notes

Some discussions hinge on the definitions of physical constants and the assumptions underlying string theory, which may not be universally accepted or fully resolved.

Spinnor
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Do we know enough of the workings of string theory to say what factors give rise to a large or small value of the velocity of propagation of massless fields for a given multiverse?

Thanks!
 
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You can see a zillion threads here asking why the speed of light is what it is, but it is essentially a unit conversion. This question is tantamount to asking if a given multiverse has eleven inches to the foot.
 
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I guess the speed of light has a definition within an individual universe, with respect to whatever "rods and clocks" (as in special relativity) exist there. Bound systems like atoms will define a natural length scale, and e.g. decay processes will define a natural time scale. So if the question is, what determines those scales for a specific string vacuum, essentially it's the value of the geometric and other moduli in that ground state - size of the extra dimensions, volume of any branes, and so on. These geometric quantities are dynamical and have a lowest-energy configuration, they determine masses and couplings of strings, and masses and couplings in turn determine the size and lifetime of particles.
 
mitchell porter said:
I guess the speed of light has a definition within an individual universe, with respect to whatever "rods and clocks" (as in special relativity) exist there.
The speed of light is derivative because it is has units. What's fundamental is the fine structure constant. If that's different then the speed of massless objects is different
 
Last edited:
Vanadium 50 said:
You can see a zillion threads here asking why the speed of light is what it is, but it is essentially a unit conversion.

Will search for those threads to try and understand why I asked a bad question.
 
There is no such thing as a bad question...just bad answers...keep on asking...!
 
phinds said:
The speed of light is derivative because it is has units.

Since Lorentz group's boosts transform spacelike vectors to timelike and vice versa, time and space axes should naturally use one unit, not two different units. Velocities in those units are dimensionless, and c = 1.
 

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